Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.
NAME
v.external - Creates a new pseudo-vector map as a link to an OGR-supported layer or a PostGIS feature table.
KEYWORDS
vector,
import,
external,
OGR,
PostGIS,
level1
SYNOPSIS
v.external
v.external --help
v.external [-ojfltb] input=string [layer=name] [where=sql_query] [output=name] [--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
- -o
- Override projection check (use current location's projection)
- Assume that the dataset has the same projection as the current location
- -j
- Perform projection check only and exit
- -f
- List supported formats and exit
- -l
- List available layers in data source and exit
- -t
- List available layers including feature type in data source and exit
- Format: layer name,type,projection check,geometry
- -b
- Do not build topology
- Advantageous when handling a large number of points
- --overwrite
- Allow output files to overwrite existing files
- --help
- Print usage summary
- --verbose
- Verbose module output
- --quiet
- Quiet module output
- --ui
- Force launching GUI dialog
Parameters:
- input=string [required]
- Name of input OGR or PostGIS data source
- Examples:
ESRI Shapefile: directory containing a shapefile
MapInfo File: directory containing a mapinfo file
PostGIS database: connection string, eg. 'PG:dbname=db user=grass'
- layer=name
- Name of OGR layer or PostGIS feature table to be linked
- Examples:
ESRI Shapefile: shapefile name
MapInfo File: mapinfo file name
PostGIS database: table name
- where=sql_query
- WHERE conditions of SQL statement without 'where' keyword
- Example: income < 1000 and population >= 10000
- output=name
- Name for output GRASS vector map (default: input layer)
v.external creates new vector map as a link to external OGR
layer or PostGIS feature table. OGR (Simple Features Library) is part
of the
GDAL library, so you need to install
GDAL to use
v.external for external OGR layers. Note that a
PostGIS feature table can be linked also using built-in
GRASS-PostGIS
data driver (requires GRASS to be built with PostgreSQL support).
The simple feature data model used by OGR (or PostGIS) is very
different from the topological format used by GRASS. Instead of true
topology, so called 'pseudo topology' is created for data linked by
v.external. User should learn the difference between those
two formats, because some modules working correctly with GRASS native
data, can produce wrong results with input vector maps created
by v.external.
Limitations:
Due to these data model differences v.external does not work
with all data formats. In general, for all formats that do not have a
key column (e.g. SHAPE file), attributes are not accessible, and attributes
would get lost when modifying the geometries. Therefore it is generally
not safe to link vector data with v.external. In many cases it
does not make sense to use v.external linked data with simple
features, instead vector data should be imported with v.import
or v.in.ogr to get true topology support. Importantly, point
cloud data which do not have topology, can be linked with v.external
as long as there are no attributes attached to these point cloud data, or
if the format of the point cloud data has a key column that allows linking
vector geometries to attributes.
See v.db.connect for an
example of maintaining attributes in external DBMS in also writable
mode.
To list supported OGR formats, type
For details see
GDAL web site.
Assuming that 'test_shape.shp' is located in directory
'/home/user/shape_data'.
v.external input=/home/user/shape_data layer=test_shape output=grass_map
By default, PostGIS links are created by built-in PostGIS support,
ie. using
GRASS-PostGIS data driver. If the environment
variable
GRASS_VECTOR_OGR exists, or GRASS is compiled
without PostgreSQL support then GRASS will use OGR-PostgreSQL driver
for creating a link.
List of layers for given data source can be printed by -l
flag.
v.external input="PG:host=localhost user=postgres dbname=postgis" -l
...
polymap
...
v.external input="PG:host=localhost user=postgres dbname=postgis" layer=polymap
Note: Authentication details (user password) can be preferably defined
by
db.login.
Assuming that 'mapinfo_test' MapInfo file is located in the current
directory (".").
v.external input=./ layer=mapinfo_test output=grass_map
Note: you have to select the CATD file
v.external input=CITXCATD.DDF output=cities
v.external input=input/2000/56015/ layer=CompleteChain,PIP output=t56015_all
By
where option only subset of features can be linked. In the
example below only one feature (in this case a vector tile) will be
linked as a new GRASS vector map.
v.external in="PG:dbname=tiles" layer=wrs2_descending where="pr=191026"
...
Number of areas: 1
...
OGR vector library C
API documentation
v.external.out,
v.clean,
v.db.connect,
v.import,
v.in.db,
v.in.ogr,
v.out.ogr
GDAL Library
PostGIS
See
also GRASS user wiki page for more examples.
Radim Blazek, ITC-Irst, Trento, Italy
PostGIS support by Martin Landa, GeoForAll (OSGeoREL) Lab, Czech
Technical University in Prague, Czech Republic
SOURCE CODE
Available at:
v.external source code
(history)
Latest change: Sat Feb 20 11:06:03 2021 in commit: eafabb743aa3bea1b4e09baf84ed860dbcd1fe2c
Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.
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GRASS Development Team,
GRASS GIS 7.8.8dev Reference Manual